我如何使用QTextBlock？

QTextBlock block = textEdit->firstCursorPosition();
int blockNumber = block.blockNumber();
int blockLength = block.length();
QTextBlock::Iterator iterator = block.begin();

QTextBlock block = textEdit->firstCursorPosition();
QTextBlock::Iterator iterator = block.begin();
while (!iterator.atEnd()) {
    QTextFragment fragment = iterator.fragment();
    QString text = fragment.text();
    iterator++;
}

QTextBlock block = textEdit->firstCursorPosition();
QTextCursor cursor(block);
cursor.insertText("Hello, world!");

QTextBlock block = textEdit->firstCursorPosition();
QTextCursor cursor(block);
cursor.select(QTextCursor::BlockUnderCursor);
cursor.removeSelectedText();